In the coolant circuit, the expansion valve causes a throttling of the coolant pressure and achieves the purpose of controlling the superheating of the coolant at the evaporator output with the goal of protecting the compressor connected after the evaporator against nonpermissible liquid contact and to effect a good degree of fill in the evaporator, which degree of fill meets the performance demands. The term "superheating" means the increased heating of the evaporated coolant beyond the evaporation temperature, which can occur only after the complete evaporation of the coolant within the evaporator. Thus by controlling the superheating, it is achieved that the evaporator is supplied with exactly the amount of liquid coolant which it can there completely evaporate due to the supply of heat thereto.
The adsorption thermosensor contains as a control filler a suitable gas or gas mixture as an adsorbate and an adsorbent consisting of a solid material with a large surface area. For example, activated carbon, silica gel or molecular sieves can be considered as adsorbents, whereas mainly CO.sub.2 and CH.sub.4 are used as an adsorbate. The adsorption of the adsorbate by the adsorbent are temperature dependent within a wide range which has an almost linear pressure/temperature characteristic, which is particularly advantageous for the superheating control with the help of a thermostatic expansion valve.
For an optimum control of a coolant circuit, care must be taken through a structural design of the expansion valve, on the one hand, and the adjustment of the adsorbent fill, on the other hand, that within a pregiven range of operation of the evaporator temperature there results an essentially constant static superheating of a select coolant, for example, 3 to 6 K at the evaporator output. The conventional thermostatic expansion valves are set at the factory for each coolant occurring in actual practice by selecting the mentioned parameters, and are, if necessary, stored until needed.
The coolants R12, R22 and R502, depending on the spectrum of use, have up to now mainly been used in commercial compression refrigeration machines. Of these coolants only R22 will be permitted in the future, and even this one only as a transition solution for a limited time period. The important reason is the--even if only small--ozone decomposing potential of these coolants. The cooling and climate control industries examine, and test in practice therefore a plurality of chlorine-free alternative coolants, which are intended to replace the mentioned standard coolants in the future. Important selection criteria are, aside from the ozone decomposing potential and the direct greenhouse potential, also the energy requirements for operating the coolants (indirect greenhouse effect).
The plurality of the available replacement coolants require, when they are used in refrigeration plants, the use of suitably designed and adjusted thermostatic expansion valves. Up to now these have each been adapted to the individual coolants by the factory, the factory also stored and, when needed, distributed these to the customer. With an increasing number of replacement coolants, of which some were only partly used experimentally, this results, however, in an increasingly vague multitude kept in storage.
Starting out from this, the basic purpose of the invention is to develop a process for setting the static superheating of an expansion valve, which enables with simple means a change over to different coolants.